Demodulator system for time modulated pulses



Ferb- 22, w49' M. G. HOLLABAUGH DEMODULTOR SYSTEM FOR TIME MODULATEDPULSES Filed April 18, 1946 .INI/ENTOR. mx a. Hama/:UGH

Patented Feb. 22, 1949 DEMODUIJATOR SYSTEM'FOR' TIME. MODUIATEDPULSESMax: G. Hollabaugln,JacksonfHeightsg.Ni asfsignor to Federal,Telecommunication Laborwtories4 Inc.,` New. York, N., Y, a'.corporationof Delaware Application April 18, 1946-', SerialifNoi.66351126;

9. Claims.

This invention` relatesA to demodulators. for time modulatedi pulsesystems, particularly.` ot the multi-channel type;

Multa-channel. time modulated: pulse systems haveV been proposed; inwhich pulses, oiv different channels are interleaved and spacedwithrespect to regularly repeated marker pulses or signals soaszto form avsingle train.A

An object of the present invention isthe provision of an improveddemodulator for time modulated pulse systems.

Anothery object of thelpresent invention. is the provision of a combineddemodulator andchannel selector for multichannel time modulated` pulsesystems.

A feature of the present invention is they provision of a combinedchannel selector and demodulator characterized. by simplicity and rerliability.

Another feature oftliepresent invention is the provision of ademodulator for timemodulated pulses Whose characteristics vary substantiallylinearly With the time modulation off the pulses.

Other andfurther objects of the-present invention willbecome apparentand the invention will be best understood from the following descriptionof an embodiment thereof, referencebeing had tov the-drawings, inwhich:V

Fig. 1 is a block diagram of a multi-channel time modulated pulsereceiver embodying my invention;

Fig. 2 isa schematic diagram of a selector-demodulator embodyingmy'invention; and

Fig. 3 isa set of curves used in describing the operation of theselector-dernodulatorV of Fig. 2.

Referring now to Fig. 1, the receiver system there shown is of the typeparticularlyl adapted for the reception of pulse trains of multi-channeltime modulated pulses such as for example, as illustratedin curve A,Fig. 3, `vvl'iere a series of signal pulses I, 2,'3, d, etc., eachforming` part of a separate'channel, follow a marker pulse 5. Theseseries are repeated as shown in said figure to form part of acontinuoustrain with the signal pulses being varied'- between the limitsindicated by the dotted lines on either side thereof. The signal pulsesare equally spaced from each other in their unmodulated position.

Such trainsv of pulses may be used to modulate a carrier'vvave which maybe radiated and thereafter received on an antenna I5 and fed to a re;-ceiver I Where the carrier frequency is removed. Theu output cfreceiveril" isfed` througrli` a plurality offchannels 8, 9, I0', II',each channel being designed tdneceiue pulses'belongingytolaseparate oneo the-pulsechannelsv I:.4. respectively.' For Control pur-poses, anadditional. channel t2; is provided attfne; output of the receivenn 1.3.Whieh channel isusedttoselect'. thesmarken-pulse asa-forenamplebr'meanszof. apulsewidth ortiine dura.- tion discriminatprorothertypeert marlieeselectcrtt', the output, oie: the; markenselectorfbeinging turn used tm synchronize aJrecta-ngulaznwave generator. le,whose-output iszthen fed` over; a line I5; tore delai/ device I6 imchannel 8; the delay device IiB.- lis adjusted-,for thel purpose; of

delaying the; centrali ware. output. of generator La to determine'.which. of the f particular channels is togbe; selected.. in theselector-demodulator` ill to.` which;i the delayed: rectangular: wavefrom: delay device Iisrfed; Fori example, infchannel' S, theselecton-demodulatorf- I1; which. receiveswall the pulses',cnly'a-ccepts those of the desired channel. which: maybek forl example,g'and de'- modulates the time modulation off the pulses vof channel Ieand; feeds. its result-ing. output to-` any suitable utilization. devicelIii The other signal channels. f, lil' andl Hf are similar to chai-melY8 in that. they. have a corresponding.. delay :device Iii?,seleet'on-demodulator 'Il' and suitable-utilisa;- tion device 53;- buttheA delays in the separate channels.Y differ to i selectdifferentpulsev` channels.

The operation of' the selectoredemodulator- I'l' will' be bestunderstood from the illustration of Fig. 2i` and the curves ofFFig; 3.Rectangular Wave generator I4 produces rectangular Wave control pulsesI9" having a repetitionv frequency equal tothe repetition frequency ofthernarker pulses and. havinga sumcient duration toaccommodaterany-signa-l'pulse-,over its entire range of timedisplacement due to modulation. For example, in. one; given case, thesignal pulse had a width or a halfmicrosecond andlhadVv a displacementof plus or minusone microsecond. The total time elapsingto cover the*signalpulse with its maximum displacement is a periodJ of two* and onehalf microseconds. The-widthof' the rectangular Wavey pulse leg wasfourV microseconds and' was adjustable; The spacina'between' pulsesl attheir central position Was five microseconds; The rectangular pulses t9Lare delayed'- a sufclent amount in delay device l5 to select theparticular channel desired; For example; referringy to curve B; Fig. 3,ther delay in delaydevice I6 was such as toselect channel 2 as'iwillbeseen since the rectangularpulse' |19 substantially coincideswith pulse2 and covers'the maximum time dis placement o saidpulse ineither-direction.

The rectangular' pulse` I9 and the signall pulses are used to controlthe output of an electron discharge device as for example by being fedto the second and first grids respectively of a pentode 20 in theselector-demodulator |1. The pentode 20 is so biased that neither therectangular pulse alone nor the signal pulse alone is su'icient to causethe flow of plate current, as is indicated by the conductivity levels 2|and 2'2 associated with vcurves A and B respectively. When, however,said rectangular wave pulse I9 coincides with one of the signal pulses,such as for example, signal pulse 2, the pentode 2U conducts and by theuse of suitable shaping means consisting of condenser 23, resistors 24and 25, the plate current i is then so shaped as to producea negativepulse 26, curve 3, Fig. 3 at the rst grid of a second pentode 21 in theselector-demodulator 1. Pulse 26 has a very steep leading edge 28 and asubstantially logarithmically-declining trailing edge 29. Therectangular pulses |9 which are applied to the second grid of pentodeare also 'simultaneously applied to the second grid of pentode 21.Pentode 21 has a low cut-off level as indicated by the line 30 so thatthe rectangular pulse I9 is sufcient to start pentode 21 conducting.When, however, pulse 26 is applied to the first grid of pentode 21,pulse 26 has so large an amplitude that it immediately cuts 01T pentode'21 despite theA fact that rectangular pulse I9 is still being appliedin a positive vectorial direction to the second grid of pentode 21. Theresultant output of pentode 21 consists of pulses 3|, Whose leading edgecoincides with the leading edge of pulses |9 and whose trailing edgelcoincides with the leading edge of pulses 26. Since the leading edge ofpulse 26 coincides with the leading edge of the signal pulse, as forexample, pulse 2 in Fig. 3, the leading edge of pulse 26 will varyaccording to the time modulation of the signal pulse and likewise thetrailing edge of pulse 3| will vary with the time modulation of thesignal pulse. This is represented in Fig. 3. For example, pulse 2 in thefirst series is represented as being in its intermediate or unmodulatedposition and the resultant output pulse 3| has a given width. Pulse 2ain the second series is represented close to one extreme of modulationand theresultant output pulse 3|a is considerably wider than pulse 3|.Pulse 2b in the third series is shown at the other extreme of modulationand the resultant output pulse 3|b is narrower than pulse 3|.Accordingly, the duration of the output pulses 3| varies in accordancewith the time modulation of the signal pulses. It will be seen that thisvariation is linear and is not determined by the transfercharacteristics of the pentode 21. `The output pulses 3| may then be fedto any suitable integration device such as for example, a 10W passiilter 32 and then to the utilization device I8 which may be forexample, an amplifier and loud speaker system. l

While I have described above the principles of my invention inconnection with specic apparatus, it is to be clearly understood thatthis description is made only by way of example and not as a limitationon the scope of my invention.

I claim:

1. A demodulator for time modulation pulse systems in which a signalpulse varies from a given time position according to its modulation,comprising a control pulse source producing pulses of constant duration,said duration being at least as great as the maximum range of timedisplacement of the signal pulses dueto modui 4 lation, means for timingone of lsaid control pulses substantially to coincide in time with acorresponding signal pulse so that the control pulse has a xed timerelationship to the unmodulated position of the signal pulse and coversthe entire range of time displacement thereof, means responsive to the'coincidence of the timed control pulse and the signal pulse to produce apulse having a relatively steep Wave front, current-control meansresponsive to the timed leading edge of the control pulse for initiatingthe flow of current and responsive to the steep pulse for halting the owof current, whereby the resultant output pulse from said current-controlmeans varies in duration in accordance with the time modulation of thesignal pulse.

2. A demodulator for time modulation pulse systems of the type in whicha marker signal is followed by a signal pulse which signal pulse variesfrom a given time position with respect to the marker signal accordingto its modulation, comprising means responsive to the marker pulse forproducing a control pulse` of constant duration, said duration being atleast as greatas the maximum range of time displacement of the signalpulses due to modulation, means for delaying said control pulse tosubstantially coincide in time with the signal pulse so that the controlpulse has a xed time relationship to the unmodulated position of thesignal pulse and covers the entire range of time displacement thereof,means responsive to the coincidence of the delayed control pulse and thesignal pulse to produce a pulse having a steep wave front,current-control means responsive to the leading edge of the delayedcontrol pulse for initiating the ilow of current and responsive to thesteep pulse for halting the ow of current, the resultant output pulsefrom said current-control means varying in duration in accordance withthe time modulation of the signal pulse, and integrating means fortranslating the duration of said' output pulse into an amplitudecharacteristic.

3. A demodulator according to claim 2 wherein said control pulseproducing means is comprised of a rectangular wave generator.

4. A demodulator according to claim 2 wherein said means responsive tothe coincidence of the delayed control pulse and the signal pulsecomprises an electron discharge device having at least oneA controlelement, means for biasing said device so that the control pulse aloneor the signal pulse alone is of insuilicient amplitude to cause saiddevice to conduct, but both signal pulse and control pulse together arecapable of causing conduction of said device, means for applying saiddelayed control pulse to a control element of said device, means forapplying said signal pulse to a control element of said device, acondenser connected to be rapidly discharged upon conduction of saiddevice to thereby produce the steep wave front of the steep pulse.

5. A demodulator according to claim 2 wherein said current control meanscomprises an electron discharge device and further including means forimpressing said delayed control pulse on said device to initiateconduction thereof, and means for impressing said steep pulse on saiddevice for halting the conduction thereof.

6. A demodulator according to claim 2 wherein said means responsive tothe coincidence of the delayed control pulse and the signal pulsecomprises an electrondischarge device having at least one controlelement biased so as to conduct upon coincidence of the control pulseand the signal pulse, means for applying said delayed control pulse to acontrol element of said device, means for applying said signal pulse toa control element of said device, a condenser connected to be rapidlydischarged upon conduction of said device to thereby produce a negativepulse having a steepvwave iront, and said current-control meanscomprises a second electron discharge device, means for impressing saidcontrol pulse on a grid of said second device to cause conductionthereof, and means for impressing the steep negative pulse upon a gridof said electron discharge device to halt conduction thereof.

7. A channel selector and demodulator for multi-channel time modulationpulse systems of the type in which a marker signal is followed by asuccession of signal pulses, each forming part of a separate channel andeach varying from a given time position with respect to the markersignal according to its modulation, comprising means responsive to themarker pulse for porclucing a control pulse of constant duration, saidduration being at least as great as the maximum range of timedisplacement of the signal pulses due to modulation, means for delayingsaid `control pulse to coincide with a pulse of the channel desired sothat the control pulse has a xed time relationship t0 the unmodulatedposition of the signal pulse and covers the entire range of timedisplacement thereof, means responsive to the coincidence of the delayedcontrol pulse and the signal pulse of the desired channel to produce apulse having a steep wave front, current-control means responsive to theleading edge of the delayed control pulse for initiating the ilow ofcurrent and responsive to the steep pulse for halting the flow ofcurrent, the resultant output pulse from said current control meansvarying in duration in accordance with the time modulation of the signalpulse of the desired channel,

6 and integrating means for translating the duration of said outputpulse into an amplitude characteristic.

8. A channel selector and demodulator according to claim 7 wherein saidmeans responsive to the coincidence of the delayed control pulse andVthe signal pulse of the desired channel comprises an electron dischargedevice having at least one control element, means for biasing saiddevice so that it conducts upon coincidence of the control pulse andsignal pulse, means for applying said control pulse and said signalpulse to control the conduction of said device, a condenser connected tobe rapidly discharged upon conduction of said device to thereby producethe steep wave front of the steep pulse.

9. A channel selector and demodulator according to claim '7 wherein saidcurrent control means comprises an electron discharge device,

means for applying said control pulse so that the leading edge thereofinitiates conduction of said device, said control pulse having aduration at least equal to the total width of the signal pulse vREFERENCES CITED The following references are of record in the ile ofthis patent:

UNITED STATES PATENTS Number Name Date 2,416,088 Deerhake Feb. 18, 19472,421,025 Grieg May 2'?, 1947

